Impulse-radio ultra-wideband (IR-UWB) transmission has recently become popular for data communications. In the new IEEE 802.15.4 a standard, IR-UWB modulation is mated with a concatenated coding scheme consisting of a Reed-Solomon and a convolutional encoder. While most of the available literature has been dedicated to the study of uncoded IR-UWB transmission, this paper is concerned with the performance analysis for IEEE 802.15.4 a compliant concatenated coded IR-UWB systems. In particular, a semi-analytical error-rate expressions for coherent RAKE detection with suboptimal multipath combining is presented. While first a single-user channel is assumed, in the second part of this paper this analysis is extended to include the effect of IR-UWB multiple access interference. To this end, a Gilbert-Elliot-type Markov interference model is adapted to the IEEE 802.15.4 a modulation format.